Chemistry 30A Midterm Exam #3 Laney College Dr Schaleger

Chemistry 30A Midterm Exam #3 Laney College Dr Schaleger

Chemistry 30A
Dr Schaleger
Midterm Exam #3
Laney College
Spring 2014
Name____________________________
1. (10 pts). Select the main intermolecular force of attraction responsible for holding together
each of the following substances in the state (solid, liquid or gas) indicated. The choices are
(A) London dispersion (induced dipole-induced dipole); (B) dipole-dipole; (C) hydrogen
bonding; (D) ion-ion (cation-anion); (E) none of the above.
a. ____ Water (l)
b. ____ Hexane, C6H14 (l)
c. ____ Nitrogen, N2 (g)
d. ____ Barium sulfate, BaSO4 (s)
e. ____ Acetonitrile, CH3CN (l)
2.
(10). A 25 mL sample of vinegar was exactly neutralized by 23.81 mL of 1.00 M NaOH.
What is the molarity of the vinegar? What is the (m/v)% of the vinegar? (Vinegar is an
aqueous solution of acetic acid, CH3COOH).
3. (9). Give a PROPER name each of the following compounds.
AlF3
H2S
(NH4)2CO3
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Chemistry 30A
Dr Schaleger
Midterm Exam #3
Laney College
Spring 2014
Name____________________________
4. (5). What is the molecular weight (to 2 significant figures) of a gas sample (0.20 L at 298 K
and 1.00 atm) that weighs 0.589 g?
5. (5). True (T) or (F) False.
a. _____The concentration of dissolved CO2 in the oceans of the world has increased over the last
several decades, resulting in an increase in the pH of the ocean.
b. _____Sodium chloride is a weak electrolyte in water.
c. _____Molarity is defined as the number of moles of solute per liter of solvent.
d. _____Dissolving sodium chloride in water lowers the boiling point of the solution.
e. _____According to Henry’s Law, the concentration of a dissolved gas decreases with increasing
external pressure.
6. (5). How many grams of solute are in 1.50 L of 0.20 M aqueous KOH?
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Chemistry 30A
Dr Schaleger
Midterm Exam #3
Laney College
Spring 2014
Name____________________________
7. (10). A. If the concentration of nitric acid, HNO3, in water is 15.0 g/L, what is the molarity?
B. What is the pH of a 0.0055 M solution of nitric acid?
8. (3). What is the formula of the conjugate base of H2PO4−?
9. (3). Consider the heat of fusion of solid sulfur, S(s)  S(l) and check one of the choices.
a. ____The process is endothermic and ΔHfusion is positive.
b. ____The process is endothermic and ΔHfusionis negative.
c. ____The process is exothermic and ΔHfusion is positive.
d. ____The process is exothermic and ΔHfusion is negative.
10. (5). What is the pH of 0.0050 M NaOH?
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Chemistry 30A
Dr Schaleger
Midterm Exam #3
Laney College
Spring 2014
Name____________________________
11. (9). Consider the acid-base reaction between nitrous acid (HONO) and sodium bicarbonate
(NaHCO3).
a. Write the balanced equation for the reaction.
b. Write the net ionic equation for the reaction.
c. Predict whether the equilibrium equation you wrote in part (a) favors the right hand side (RHS) or
the left hand side (LHS). (See Appendix).
12. (5). What is the pH of a buffer solution of NH4Cl (0.20 M) and NH3 (0.10 M)? (Hint: What is
the equation defining Ka?).
13. (4). Which aqueous solution has the lowest freezing point: ______0.5 M ethylene glycol
(HOCH2CH2OH); _____0.5 M sodium chloride; or _____0.5 M calcium chloride (CaCl2)?
14. (3). The roots of a Giant Sequoia tree take up water from the soil and transport it to the treetop,
as much as 300 feet above ground level. What is the technical term for this process, also
known as “root pressure”?
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Chemistry 30A
Dr Schaleger
Midterm Exam #3
Laney College
Spring 2014
Name____________________________
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Chemistry 30A
Dr Schaleger
Midterm Exam #3
Laney College
Spring 2014
Name____________________________
15. (5). One mole of any gas at STP occupies what volume?
16. (5). If 1.5 L of nitrogen (N2) and 4.5 L of hydrogen (H2) at STP react to give ammonia (NH3)
at STP, what volume of ammonia gas at STP is formed? (Hint: Write the balanced equation).
17. (4). Write the equation for the hydrolysis (reaction with water) of sodium acetate (NaOAc),
the salt of a weak acid, in aqueous solution. (Net ionic is OK).
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Chemistry 30A
Dr Schaleger
Midterm Exam #3
Laney College
Spring 2014
Name____________________________
Appendix
R = 0.082 L-atm/mol-K
Abbreviated table of Brønsted acids
Acid
Ka
pKa
H2SO4
LARGE
LG negative
H3O+
55.5
-1.74
HSO4−
1.2 x 10-3
-2.08
4.5 x 10
-4
3.35
1.8 x 10
-5
4.74
H2CO3
4.3 x 10
-7
6.37
NH4+
5.6 x 10-10
9.25
HCN
4.9 x 10-10
9.31
HCO3−
5.6 x 10 -11
10.75
H2O
10-14
14
HONO
HOAc
Scoring
1. (10) _____
11. (9) _____
Class Median _______
2. (10) _____
12. (5) _____
Median Adjusted Score ______
3. (9) _____
13. (4) _____
Your Adjusted Score ______
4. (5) _____
14. (3) _____
Your Letter Grade _____
5. (5) _____
15. (5) _____
6. (5) _____
16. (5) _____
7. (10) _____
17. (4) _____
8. (3) _____
9. (3) _____
TOTAL (100)________
10. (5) _____
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